There has been much discussion on the
Internet about the use of dipolar and bipolar speakers in home
theater configurations. The planar-magnetic design represents the
dipolar speaker in its purest sense, as the ribbon is open at the
front and the back in an equal manner. Usually, a cone woofer is
also used, because the ribbon cannot move enough air at low
frequencies. In the case of the Ambience, the woofer is a 7"
long throw cone in a 23 liter bass reflex enclosure (MDF painted
black) tuned to 32 Hz. The 2" flared port is on the rear.
The crossover frequency is at 420 Hz. This is higher than some
other planar magnetic models, and the result, in our opinion, is
that the ribbons will last longer (the ribbons tend to stretch
out with use over the years, attenuating their accuracy).
Planar-magnetic ribbon speakers work on the principle of having a
corrugated metal foil strip that is suspended tightly between
powerful permanent magnets. There are two types of
planar-magnetic speakers. One, the true ribbon speaker, has the
foil itself suspended with tension at the ends of the foil. The
other, called quasi-ribbon, has the foil attached to a plastic
membrane, and it is the membrane that is suspended with tension
at the ends. The quasi-ribbon is sturdier, but it has less high
end transient response, because the total mass of the foil and
plastic membrane is greater than just the foil, and it cannot
respond as quickly. The Antony Moore is a true ribbon speaker.
When the musical signal current flows through the foil, the
magnetic field created around the foil causes the foil to be
attracted or repelled by the permanent magnets depending on which
direction the current is flowing in the foil. The movement of the
foil back and forth creates the sound. This is called a line
source driver.

One has to have a taste for not only the
dipolar sound, but planar-magnetic designs in order to appreciate
a speaker like the Ambience. We have long had a taste for both,
and the Ambience is a superb example of the best that such
speakers can be. Planar-magnetics can be had for much less money,
but the craftsmanship on the Ambience is worth the extra price.
Our review units had solid planks of Australian Hardwood stained
to Rosewood, serving as the frame. Hardwood veneer is expensive,
but solid planks of it? Wow! In Australia, it is against the law
to cut down native wild rosewood trees for use in furniture (can
you blame them?), so other hardwood trees are grown specifically
for this use. The difference is that the wild trees are much
older and have a deeper color to them. The grown-for-furniture
trees have the grain, but not the deep color. So, by application
of stain in the finishing stage, the color of the wild tree is
approached. That is what was done to our review samples.
Specifically, they are made from "Shining Gum" stained
to the Wild Australian Rosewood color. The speakers are large
enough, that photographing them from a distance to show the
entire speaker would not do them justice. Therefore, we took our
photo up close with the reflected light angled so that you can
see not only the grain texture, but the deep color (see photo).
By window light, they appear almost violet, but by incandescent,
they are burgundy, and exquisite.

Most of us here like deep bass, and I
assumed that a 7" woofer would not really deliver the kind
of bass that we prefer. Also, I did not think I would like the
crossover at 420 Hz, since the cone woofer would be carrying a
good proportion of the human voice spectrum (male voices anyway).
I argued these points before we even accepted the offer to review
the speakers, but we were reassured to just wait until we heard
them for ourselves. We were not disappointed.

The Ambience speakers have very high
resolution of detail, significantly more than our reference
planar-magnetics. In fact, our reference speakers sounded a bit
nasal when compared directly, and of course were much deeper in
the bass region because they have four 12" woofers (dipolar
arrangement) in each speaker. However, the bass in the Ambience
was much tighter and cleaner. The sound stage of the Ambience
extended about 3 feet on either side of the panels, when the
speakers were 8 feet apart and toed in at 15 degrees. And, like
all planar-magnetics, they have a very deep sound stage from
front to back. They need to be several feet out from the wall to
achieve this.

Voices were very natural. No chestiness,
even with the cone driver handling those pesky 120 Hz frequencies
in an enclosure that was not heavily damped. Tony Bennett and
Enya never sounded better. Like all line drivers, we could hear
the high frequencies beating if we moved our heads vertically.
This occurs because the entire length of the ribbon is emitting
the sound, and the waves interact, causing augmentation and
cancellation, depending on where the listener is. They are also
very dependent on room acoustics, so careful placement is
necessary. All dipoles are like this. The woofer produced some
audible harmonics when <20 Hz sine waves were played through
the speaker.

These speakers are great in the home
theater environment. Line drivers produce an incredible sound
stage for movies, and, for example, in the early minutes of
"The Return of the Jedi" where Vader emerges from his
ship after landing in the space port, the sounds of the steam
were presented in a way that a conventional speaker just cannot
do. Of course, the driver has to be able to really take the
intense movie sound track signal and deliver without harshness.
The Ambience delivers, and how! Just make sure you have plenty of
muscle to drive them though, as they have a relatively low
sensitivity (86 dB/w/m).

Frequency Response Tests were performed. It
should be noted that with dipoles, half the sound energy is
emitted from the rear, so any response test is complicated with
the room acoustics, no matter how close the microphone is placed
to the speaker. The response test results were as follows:

Near Field, one meter, left channel only,
microphone on axis with center of panel:

In summary, the Ambience hybrid
planar-magnetic speakers are superb. The price is steep, but the
construction quality warrants it, and although they may have been
designed with CDs in mind, laserdiscs can really strut their
stuff with these babies next to the "tube". Count me
in.